This application is based on Application No. 2000-342082 filed in Japan on Nov. 9, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an energy-saving type of elevator controller to which a secondary battery is applied.
2. Description of the Related Art
FIG. 7 is a diagram showing the system configuration of a conventional elevator controller.
The elevator controller shown in FIG. 7 uses an ordinary utility power supply 1 for supplying a three-phase alternating current or the like, and an electric motor 2, such as an induction motor. The electric motor 2 rotates to drive a hoist machine 3, which moves, along a vertical direction, a car 5 and a counterweight 6 connected to two ends of a rope 4 to transport passengers in the car to a designated floor.
AC power supplied from the utility power supply 1 is rectified by a converter (CNV) 11 constituted of diodes, or the like, and converted into dc power. The dc power is supplied to a dc bus 9. The dc power is converted into variable-voltage variable-frequency ac power by an inverter (INV) 15 constituted of ordinary transistors, insulated gate bipolar transistors (IGBTs), or the like.
A controller 8 constituted of a microcomputer, or the like, controls the entire elevator system. The controller 8 prepares elevator start and stop commands and elevator position and speed commands. An inverter control circuit 13 drives and rotates the electric motor 2 on the basis of information on current feedback from a current sensor 12 and speed feedback from a speed sensor 7 mounted on the hoist machine 3 and constituted of an encoder, or the like, and on the basis of commands from the controller 8, thereby achieving position and speed control of the elevator. For this control, the inverter control circuit 13 controls the output voltage and output frequency of the inverter 15 through a gate drive circuit 14.
The counterweight 6 of the elevator is set to a weight such as to be balanced with the car 5 with a moderate load (ordinarily half the rated load). Ordinarily, therefore, the operation is in a power-drive mode in which electric power is consumed when the car moves downward without a load, and in a regenerative mode in which kinetic energy is converted into electric power when the car moves upward without a load. Conversely, the operation is in the regenerative mode when the car moves downward with the rated load, and in the power-drive mode when the car moves upward with the rated load. In ordinary elevators, electric power regenerated in the regenerative mode is consumed by being converted into thermal energy in a regeneration resistor 16 controlled by a regeneration resistance control circuit 17.
Ordinarily, an energy-saving type of elevator to which a secondary battery is applied has a power accumulator 21 using a lead-acid battery or a nickel metal hydride battery as a secondary battery, a charging and discharging circuit 22 constituted of a DC-DC converter, etc., a charging and discharging control circuit 23 for controlling electric power charged or discharged by the charging and discharging circuit 22, and a required-power computation circuit 24 for computing necessary power for the elevator and controlling the charging and discharging control circuit 23 so that the power accumulator 21 is discharged to supply a deficiency in the necessary power not fully supplied from the utility power supply 1.
In general, for the purpose limiting the size and price of the controller, the number of cell units of the secondary battery is set to a small number, so that the output voltage of the batteries is lower than the voltage of the dc bus 9. The voltage of the dc bus 9 is ordinarily controlled so as to be maintained generally at a voltage obtained by the converter 11 rectifying the current from the utility power supply 1. Therefore, it is necessary to increase the busside output voltage of the charging and discharging circuit 22 to the bus voltage during discharging of the battery, and to reduce the bus-side input voltage of the charging and discharging circuit 22 below the converter output voltage during charging of the battery. For this reason, a DC-DC converter is used as charging and discharging circuit 22. Discharging gate and charging gate control of this DC-DC converter is performed by the charging and discharging control circuit 23.
FIG. 8 is a block diagram showing an example of the above-described charging and discharging control circuit 23.
The charging and discharging control circuit 23 shown in FIG. 8 has a charging power control circuit comprised of a voltage controller 31, a charging current controller 32, a pulse-width modulation (PWM) signal circuit 33, and a gate drive circuit 34, and a discharging power control circuit comprised of a discharging current controller 41, a PWM signal circuit 42, a gate drive circuit 43, and a divider 44.
In the charging power control circuit, the voltage controller 31 computes, by proportional integration, for example, a deviation of a voltage feedback signal of the dc bus 9 from a voltage command from the controller shown in FIG. 7, and outputs the deviation as a charging current command value. The charging current controller 32 computes, by proportional integration, for example, a deviation of a current feedback signal from the current sensor 10 provided between the power accumulator 21 and the charging and discharging circuit 22 shown in FIG. 7 from the charging current command from the voltage controller 31, and outputs the deviation as a charging control command value. The PWM signal circuit 33 forms a control signal for PWM control of the charging and discharging circuit 22 comprised of a DC-DC converter on the basis of the charging control command value from the charging current controller 32, and outputs the control signal. The gate drive circuit 34 controls the charging gate of the charging and discharging circuit 22 on the basis of the control signal from the PWM signal circuit 33.
When electric power is regenerated from the electric motor 2, the voltage of the dc bus 9 is increased by the regenerated electric power. When the voltage of the dc bus 9 becomes higher than the output voltage from the converter 11, power supply from the utility power supply 1 is stopped. When the voltage of the dc bus 9 is further increased to reach a predetermined voltage, the polarity of the charging current command value from the voltage controller 31 is inverted and the power accumulator 21 is charged with the regenerated power under the control of the charging and discharging control circuit 23.
On the other hand, in the discharging power control circuit, the divider 44 outputs, from the output of the required power computation circuit 24, which computes the necessary power for the elevator, a discharging current command value so that the power accumulator 21 discharges and supplies the necessary power not fully supplied from the utility power supply 1. That is, this discharging current command value is obtained by dividing a power deviation value by the battery voltage of power accumulator 21. The power deviation value can be obtained from the utility power corresponding to the command value from the controller 8 designating the maximum supply of the utility power supply and the output power from the required power computation circuit 23. The discharging current controller 41 computes, by proportional integration, for example, the difference between the discharging current command value and the current feedback signal from the current sensor 10, which is connected between the power accumulator 21 and the charging and discharging circuit 22, as shown in FIG. 7. The discharging current controller 41 outputs the difference as a discharging control command value. The PWM signal circuit 42 generates a control signal for PWM control of the charging and discharging circuit 22, including a DC-DC converter, based on the discharging control command signal from the discharging current controller 41, and outputs the control signal. The gate drive circuit 43 controls the discharging gate and the charging and discharging circuit 22 based on the control signal from the PWM signal circuit 42.
During power-drive operation, the elevator requires supply of electric power and is supplied with the necessary power from discharge of the power accumulator 21 and from the utility power supply 1. The divider 44 outputs, from the output from the required power computation circuit 24 that computes the necessary power for the elevator, the discharging current command value to discharge the power accumulator 21 to supply a deficiency in the necessary power not fully supplied from the utility power supply 1. Thus, electric power is discharged from the power accumulator 21 under the control of the charging and discharging control circuit 23, and the bus voltage settles down at a suitable level, thereby supplying the elevator with the necessary electric power.
As described above, regenerated electric power is accumulated in the power accumulator 21 to enable reuse of original power, thus achieving an energy-saving effect.
In the above-described conventional elevator controller, there is a need to incorporate, as power accumulator 21, a high-priced large-capacity power accumulator capable of being charged by regenerated power under all possible conditions with respect to the temperature and the amount of charge (state of charge: SOC) of the power accumulator, etc. Also for the purpose of ensuring a sufficient amount of discharge under such conditions, a high-priced large power accumulator is needed.
In view of the above-described problem of the conventional art, an object of the present invention is to provide an elevator controller arranged to maintain an energy-saving effect based on charging and to achieve a high energy-saving effect while using a low-capacity and low-priced secondary battery.
According to one aspect of the present invention, there is provided an apparatus for controlling an elevator, comprising: a converter for converting an alternating current from an alternating current power supply into a direct current power by rectifying the alternating current; an inverter for driving an electric motor by converting the direct current power from the converter into variable-voltage variable-frequency alternating current power, the electric motor being driven for the operation of an elevator; a power accumulator connected to a direct current bus between the converter and the inverter, the power accumulator being capable of accumulating direct current power from the direct current bus during regenerative operation of the elevator, and also capable of supplying the accumulated direct current power to the direct current bus during power-drive operation of the elevator; charge/discharge control means for controlling each of charging and discharging of the power accumulator from or to the direct current bus; and measuring means for measuring at least one of temperature, current and voltage of the power accumulator, wherein the charge/discharge control means adjusts the maximum value of the current for each of charging and discharging of the power accumulator according to an output from the measuring means.
In a preferred form of the invention, the output from the measuring means is a function of at least one of current, voltage and temperature of the power accumulator during charging and discharging.
In another preferred form of the invention, the state of charge stored in the power accumulator is grasped from the output from the measuring means before the power accumulator is overcharged or overdischarged to adjust charging and discharging.
In a further preferred form of the invention, the charged amount of one of a fully-charged state and a completely-discharged state of the power accumulator is grasped from at least one of the outputs from the measuring means.
In a still further preferred form of the invention, the charge/discharge control means includes, as means for adjusting the maximum value of the current for each of charging and discharging, a current value limit circuit for limiting a charging/discharging current command value to a certain charging/discharging current limit value according to the output from the measuring means.
In a yet still further preferred form of the invention, the current value limit circuit multiplies the charging/discharging current command value by a constant such that the maximum value of the charging/discharging current to or from the power accumulator supposed from the elevator operation is limited to the charging/discharging current limit value.
In a furthermore preferred form of the invention, the current value limit circuit limits the charging/discharging current command value to the charging/discharging current limit value when the charging/discharging current command value exceeds the current limit value.
In a still further preferred form of the invention, the current value limit circuit sets the charging/discharging current limit value to a value obtained as the product of a constant and one of a battery specification value and a battery rated value of the power accumulator.
The above and other objects, features and advantages of the present invention will be more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the invention taken in conjunction with the accompanying drawings.